Use better heuristic for when to apply statusbar customization during predictive back

Bug: 341921089
Flag: ACONFIG com.android.window.flags.predictive_back_system_anims NEXTFOOD
Test: Manual, i.e. verifying on device that the color switch happens when the closing window passes the middle of the statusbar
Change-Id: I7116a3808880ed504f8d41b0ba97f16406992e8c